T cells represent and essential part of our immune system in so far as their recognition system seems to detect cells that the body thereby perceives as foreign. Such cells clearly include the body's own infected cells, but may also include tumor cells if such cells present novel antigens in the context of self major histocompatibility antigens. The mechanism by which T cells effect this seemingly complex recognition remains a mystery. Recently, this mystery has been intensified by the finding of a novel, immunoglobulin-like gene family, which rearranges specifically in T cells, but whose function is unknown. This gene family is termed gamma. The proposal is to examine whether gamma expression in the mouse is, as has been claimed, specific to immature thymocytes and T cells, we shall do this by using various methods to activate mature T cells, and then to monitor for possible induction of gamma expression. A complementary approach to understanding the role of gamma, is to introduce the gene into various cells, and then to monitor in which cells it is expressed. Will there be an alteration of phenotype in a cell that expresses, de novo, an exogenously-added gamma gene? Rearranged gamma have been cloned, and it is hoped to employ them in this study. Finally, we seek to understand the nature of DNA sequence that we detect in the mouse genome, that hybridise to gamma DNA at low stringency. Perhaps they are further members of the gamma gene family.